Breast Cancer Screens Reduce Mortality

May 2, 2003

New studies of breast cancer screening programs in two European countries have found that the mammography cut the number of deaths from breast cancer by almost half, reports the British Medical Journal.

The first study, in Lancet, compared deaths from breast cancer in two Swedish counties in the 20 years before screening was introduced, 1958 to 1977, with the 20 years after, 1978 to 1997

The study of 210,000 women showed that the unadjusted risk of death from breast cancer dropped after the introduction of screening by 23 percent in women aged 40-69 years.

The mortality reduction was even greater after adjusting for age, self selection bias and changes in the incidence of breast cancer.

Also, for the first time, the study found that screening younger women reduces mortality: among women aged 40 to 49 years who were screened, breast cancer deaths fell by 48 percent compared with a 19 percent reduction in women who were not screened (presumably due to factors other than screening).

But, in contrast, no reduction in breast cancer mortality was seen in women aged 20-39 years.

The study appears to settle the argument that has previously surrounded the value of mammography screening. A meta-analysis of seven randomized trials of screening mammography published in 1991 claimed there was no reliable evidence to support the value of mammography.

A second study in Lancet, from the Netherlands, found similar results. Mortality among women aged 55 to 74 years was 20 percent lower in 2001 than in 1986-8, before screening programs were introduced.